Seeking to ease alarm over the issue, China said it attached "great importance" to freedom of navigation in waters that have some of the world's busiest shipping lanes.

New rules that take effect on January 1 will allow police in the southern Chinese province of Hainan to board and seize control of foreign ships which "illegally enter" Chinese waters, the official China Daily said on Thursday.

Surin Pitsuwan, secretary-general of the Association of Southeast Asian Nations (ASEAN), said the Chinese plan was a "very serious turn of events".